This invention relates to a process for solubilizing low molecular weight formaldehyde oligomers of 6-100 carbon atoms without contaminating the solution product with undesirable by-products of formaldehyde or the solvent. The resultant solution can be used in the production of hydroxyacetic acid (HAA), or the formaldehyde can be distilled from the mixture for reuse.
Formaldehyde has for years been produced and shipped as a 35-60% aqueous solution. Usually a minor amount of a stabilizer such as a polythiol is added. Freshly prepared formaldehyde is low molecular weight and soluble. However, on standing formaldehyde polymerizes to insoluble forms that resist dissolution. These insoluble forms are oligomers of 6 to as many as 100 carbon atoms. These polymers are tough and resistant solids that can foul heat exchanger surfaces, pumps and distillation columns, causing periodic shut-downs and dismantling to clean the production equipment. Also the formaldehyde may polymerize and solidify in the bottom of storage tanks and in shipment, resulting in loss of the shipping container as well as the formaldehyde product. Complete rail tank cars of formaldehyde may solidify.
Heating molecules of up to 5 carbon atoms will dissolve them, but molecules of 6 or more carbon atoms cannot be dissolved by simple heating. Heretofore it has been the practice to chip out the solid, but this is ineffective with process equipment and small tanks. Alternatively, caustic or ammonium hydroxide has been used to dissolve the oligomer. This technique gives a non-usable solvent-contaminated solution of high volume that cannot be incinerated because of salt content, or the ammonium prevents discharge to a waste water treatment plant. The use of HAA in accordance with the present invention allows the use of both of these waste disposal methods if desired..
Formic acid has also been used to solubilize paraform, but its corrosiveness to production equipment greatly limits its use. See German Patents 2,652,072; 2,652,003; and 2,741,505 to Hoechst A.G.
Walker ("Formaldehyde", ACS Monograph Series, Reinhold Publishing Corp., 1964, p. 153) states that strong acids will dissolve formaldehyde but pH's of 2-6 are ineffective. Thus, the effectiveness of HAA is surprising.